2002/03/21 01:19:34

[org.ibex.core.git] / src / org / xwt / util / Queue.java

diff --git a/src/org/xwt/util/Queue.java b/src/org/xwt/util/Queue.java
new file mode 100644 (file)
index 0000000..f923db3
--- /dev/null
+++ b/src/org/xwt/util/Queue.java
@@ -0,0 +1,81 @@
+// Copyright 2002 Adam Megacz, see the COPYING file for licensing [GPL]
+package org.xwt.util;
+
+/** A simple synchronized queue, implemented as an array */
+public class Queue {
+
+    public Queue(int initiallength) { vec = new Object[initiallength]; }
+    
+    /** The store */
+    private Object[] vec;
+    
+    /** The index of the first node in the queue */
+    private int first = 0;
+    
+    /** The number of elements in the queue; INVARAINT: size <= vec.length */
+    private int size = 0;
+    
+    /** Grow the queue, if needed */
+    private void grow(int newlength) {
+        Object[] newvec = new Object[newlength];
+        if (first + size > vec.length) {
+            System.arraycopy(vec, first, newvec, 0, vec.length - first);
+            System.arraycopy(vec, 0, newvec, vec.length - first, size - (vec.length - first));
+        } else {
+            System.arraycopy(vec, first, newvec, 0, size);
+        }
+        first = 0;
+        vec = newvec;
+    }
+
+    /** The number of elements in the queue */    
+    public int size() { return size; }
+    
+    /** Empties the queue */
+    public synchronized void flush() {
+        first = 0;
+        size = 0;
+        for(int i=0; i<vec.length; i++) vec[i] = null;
+    }
+
+    /** Add an element to the queue */
+    public synchronized void append(Object o) {
+        if (size == vec.length) grow(vec.length * 2);
+        if (first + size >= vec.length) vec[first + size - vec.length] = o;
+        else vec[first + size] = o;
+        size++;
+        if (size == 1) notify();
+    }
+    
+    /** Remove and return and element from the queue, blocking if empty. */
+    public Object remove() { return remove(true); }
+
+    /** Remove and return an element from the queue, blocking if
+        <tt>block</tt> is true and the queue is empty. */
+    public synchronized Object remove(boolean block) {
+
+        while (size == 0) {
+            if (!block) return null;
+            try {
+                wait();
+            } catch (InterruptedException e) {
+            } catch (Exception e) {
+                if (Log.on) Log.log(this, "exception in Queue.wait(); this should never happen");
+                if (Log.on) Log.log(this, e);
+            }
+        }
+        
+        Object ret = vec[first];
+        first++;
+        size--;
+        if (first >= vec.length) first = 0;
+        return ret;
+    }
+
+    /** Returns the top element in the queue without removing it */
+    public synchronized Object peek() {
+        if (size == 0) return null;
+        return vec[first];
+    }
+
+}